This invention is related to a process and an apparatus for removing water from tars and/or hydrocarbon oils. More particularly, this invention is related to a process and an apparatus for dehydrating tars and/or hydrocarbon oils, such as coal tar distillates, and creosote wood preserving solutions in an energy, environmental, and operationally efficient manner.
Generally, water can be removed from tars and hydrocarbon oils by heating, distillation, evaporation, vacuum dehydration, or by chemical action. Whether one method is used rather than another depends on several factors, such as the quantity of water to be removed, the types of chemicals present in the solution from which the water is to be removed, and the difficulty of removing water from the solution.
Because of the growing concern against the deterioration of the environment, chemical plants and processing plants using chemicals must conduct their activities in such a manner as to reduce exposing noxious chemicals to the environment. Therefore, the dumping of tar and/or hydrocarbon oils or derivatives thereof into large ponds or lagoons for disposal or for removal of waste by evaporation is no longer an acceptable practice. Also, dumping of effluents or used organic processing solutions containing tar and/or hydrocarbon oils into rivers or ditches for disposal is no longer an acceptable practice. In addition, according to current economics it is more feasible to recover tars and/or hydrocarbon oils or processing solutions containing them rather than disposing of them.
Removal of water from tars, hydrocarbon oils or processing solutions containing them while recovering the tar and/or hydrocarbon oil with a reduced water content can be accomplished in an enclosed vessel in order not to adversely affect the environment with noxious fumes or other discharges. The use of an enclosed vessel in the evaporation, distillation, or dehydration of water from a tar and/or hydrocarbon oil or processing solution containing them can be troublesome if the heating mechanism is inside the enclosed vessel and the tar and/or hydrocarbon oil or processing solution containing them has a tendency to form solids or semisolid material, i.e., cokes or coagulates, when subjected to heat. With these types of tars and/or hydrocarbon oils or processing solutions containing them, the thermal efficiency of the heating mechanisms in the enclosed vessels is reduced by deposition of the solid or semisolid material on the surfaces of the heating mechanisms. The heating mehanisms cannot be readily removed for cleaning from the enclosed vessel containing the tar or hydrocarbon oil. A resulting loss of efficiency from shutting down the process to remove the heating mechanisms would be difficult to overcome or reverse.
An example of such a troublesome situation exists for the material derived from coal tar and known as creosote. Creosote consists principally of liquid and solid aromatic hydrocarbons. A more precise definition of creosote is that it consists of the 200.degree.-400.degree. C. boiling fraction oof coal tar distillate produced by the high temperature carbonization of bituminous coal. The main constituents of creosote consist of (1) tar acids such as phenol, cresol and xylenol, etc.; and (2) tar bases such as pyridine, quinoline and acridine; and (3) neutral oils such as a mixture of naphthalene, anthracene, and other neutral hydrocarbons. Creosote has been used for many years to preserve wood from decay and biological attack. Inevitably, fresh creosote to be used in preserving wood will contain a small undesired amount of water, and used creosote, which has been used in a treating process to preserve wood, will contain the water originally present in the fresh creosote plus any water picked up in the treating process. The buildup of water in the creosote restricts the reuse of the creosote to treat wood; therefore, it is beneficial to remove some of the water from fresh creosote and from used creosote by dehydration so that the undesirable amount of water in the fresh creosote can be removed and so that the used creosote can again be used to treat wood.
Current dehydrators are genrally tanks with heating coils located inside the tanks. These dehydrators have several disadvantages, such as being energy intensive and creating large amounts of objectionable odors. Also, many times they operate for too long a period of time and end up driving off lighter fractions of the creosote. Also, the traditional location of the heating coils inside the tank cause the coils to coke up badly with a proportional decrease in heating ability and efficiency.